KnowledgeBase Archive

An Archive of Early Microsoft KnowledgeBase Articles

View on GitHub

Q111502: BUG: SUBSTR Index Past End of String Incorrectly Assembles

Article: Q111502
Product(s): Microsoft Macro Assembler
Version(s): 6.0,6.0a,6.0b,6.1,6.11,6.1a
Operating System(s): 
Keyword(s): 
Last Modified: 06-MAY-2001

-------------------------------------------------------------------------------
The information in this article applies to:

- Microsoft Macro Assembler (MASM), versions 6.0, 6.0a, 6.0b, 6.1, 6.1a, 6.11 
-------------------------------------------------------------------------------

SYMPTOMS
========

MASM 6.x will incorrectly assemble the SUBSTR directive and not generate the
expected error if the index value is 1 (one) greater than the length of the
string. The expected error is:

  A2091: index value past end of string

STATUS
======

Microsoft has confirmed this to be a problem in the Microsoft Macro Assembler
(MASM) versions 6.x. We are researching this problem and will post new
information here in the Microsoft Knowledge Base as it becomes available.

MORE INFORMATION
================

The sample code below illustrates this behavior as well as the correct use of
SUBSTR.

The SUBSTR directive selects a value from a string and assigns it to a symbol.
The index value (start value) cannot be greater than the length of the string.
The format of the directive is:

  <name> SUBSTR <string>, <index>

-or-

  <name> SUBSTR <string>, <start>, <length>

The directive is documented on pages 246-247 of the MASM 6.1x "Programmer[ASCII
146]s Guide."

Sample Code
-----------

  ; Assemble options needed: /c /Fl
  .model small
  .data
     op1 substr <12345678>,8  ;  4
     op2 sizestr op1          ;  5

     op3 substr <12345678>,9  ;  7 - should be A2091 here
     op4 sizestr op3          ;  8 - should be A2006 here

     op5 substr <12345678>,10 ; 10 - A2091 here
     op6 sizestr op5          ; 11 - A2006 here
  END

  Assembling this will correctly generate two errors (A2091 and A2006) on
  lines 10 and 11 as shown in the following (partial) listing. These errors
  should also be generated on lines 7 and 8 of the source, but aren't, and
  the value 0 (zero) is incorrectly assigned to symbol op4.

                 ; Assemble options needed: /c /Fl
                 .model small
   0000          .data
   = 8              op1 substr <12345678>,8  ;  4
   = 0001           op2 sizestr op1          ;  5

   =                op3 substr <12345678>,9  ;  7 - should be A2091 here
   = 0000           op4 sizestr op3          ;  8 - should be A2006 here

                    op5 substr <12345678>,10 ; 10 - A2091 here
  test.asm(10): error A2091: index value past end of string
                    op6 sizestr op5          ; 11 - A2006 here
  test.asm(11): error A2006: undefined symbol : op5
                 END

Additional query words: 6.00 6.00a 6.00b 6.10 6.10a buglist6.10 buglist6.10b buglist6.11 buglist6.00 buglist6.00b buglist6.00a

======================================================================
Keywords          :  
Technology        : kbMASMsearch kbAudDeveloper kbMASM600 kbMASM610 kbMASM611 kbMASM610a kbMASM600a kbMASM600b
Version           : :6.0,6.0a,6.0b,6.1,6.11,6.1a

=============================================================================

THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY.